Studies on the origin of the methylsulfonyl‐containing metabolites from propachlor

Abstract

Metabolites in which the chlorine from propachlor has been replaced by a cysteine group or a methylsulfonyl group [‐S(O₂) CH₃] are present in the urine of rats dosed orally with propachlor. In the present study, urine from rats given single oral doses of ³⁵S‐labeled cysteine conjugate of propachlor contained metabolites having the methylsulfonyl groups labeled with S. No metabolites containing ¹⁴C‐labeled methylsulfonyl groups were isolated from urine of rats given single oral doses of the cysteine conjugate of propachlor in which the cysteine group was uniformly labeled with ¹⁴C. These findings show that the cysteine conjugate of propachlor is the source of sulfur in the methylsulfonyl‐containing metabolites. Therefore, we suggest that a C‐S lyase present in the animal cleaves the cysteine conjugate of propachlor and thus allows further metabolism of the sulfur to a methylsulfonyl moiety.